Exploring tunneling ESEEM beyond methyl groups in nitroxides at low temperatures.

Tunneling of methyl rotors coupled to an electron spin causes magnetic field independent electron spin echo envelope modulation (ESEEM) at low temperatures. For nitroxides containing alkyl substituents, we observe this effect as a contribution at the beginning of the Hahn echo decay signal occurring on a faster time scale than the matrix-induced decoherence. The tunneling ESEEM contribution includes information on the local environment of the methyl rotors, which manifests as a distribution of rotation barriers () when measuring the paramagnetic species in a glassy matrix.

Probing structural and dynamic properties of MAPbCl hybrid perovskite using Mn EPR.

Hybrid methylammonium (MA) lead halide perovskites have emerged as materials exhibiting excellent photovoltaic performance related to their rich structural and dynamic properties. Here, we use multifrequency (X-, Q-, and W-band) electron paramagnetic resonance (EPR) spectroscopy of Mn impurities in MAPbCl to probe the structural and dynamic properties of both the organic and inorganic sublattices of this compound. The temperature dependent continuous-wave (CW) EPR experiments reveal a sudden change of the Mn spin Hamiltonian parameters at the phase transition to the ordered orthorhombic phase indicating its first-order character and significant slowing down of the MA cation reorientation.

Quantifying methyl tunneling induced (de)coherence of nitroxides in glassy -terphenyl at low temperatures.

The low-temperature Hahn echo decay signal of the pyrroline-based nitroxide H-mNOHex in -terphenyl (OTP) shows two contributions on distinct time scales. Tunneling of the nitroxide's methyl groups cause electron spin echo envelope modulation (ESEEM) on a faster time scale compared to the slower matrix-induced decoherence contribution arising from nuclear pair ESEEM. Here we introduce the methyl quantum rotor (MQR) model that describes tunneling ESEEM originating from multiple methyl rotors coupled to the same electron spin.

Probing Methyl Group Tunneling in [(CH)NH][Zn(HCOO)] Hybrid Perovskite Using Co EPR.

At low temperature, methyl groups act as hindered quantum rotors exhibiting rotational quantum tunneling, which is highly sensitive to a local methyl group environment. Recently, we observed this effect using pulsed electron paramagnetic resonance (EPR) in two dimethylammonium-containing hybrid perovskites doped with paramagnetic Mn ions. Here, we investigate the feasibility of using an alternative fast-relaxing Co paramagnetic center to study the methyl group tunneling, and, as a model compound, we use dimethylammonium zinc formate [(CH)NH][Zn(HCOO)] hybrid perovskite.

Neural networks in pulsed dipolar spectroscopy: A practical guide.

This is a methodological guide to the use of deep neural networks in the processing of pulsed dipolar spectroscopy (PDS) data encountered in structural biology, organic photovoltaics, photosynthesis research, and other domains featuring long-lived radical pairs and paramagnetic metal ions. PDS uses distance dependence of magnetic dipolar interactions; measuring a single well-defined distance is straightforward, but extracting distance distributions is a hard and mathematically ill-posed problem requiring careful regularisation and background fitting. Neural networks do this exceptionally well, but their "robust black box" reputation hides the complexity of their design and training - particularly when the training dataset is effectively infinite.